Development of a technique to quantify the effectiveness of enrichment regimes in recovering "stressed" Listeria cells.

A rapid, reliable microwell plate method based on the most probable number (MPN) technique was used to determine the effectiveness of five enrichment regimes in the recovery and enumeration of Listeria spp. cells from five seafood products. The products tested were chosen to reflect conditions under which cells were exposed to the "stresses" associated with a variety of food-processing techniques, such as treatments involving an ethanol-based marinade, lowered pH (acetic acid), heat, sugar and salt brine (Gravilax), or frozen storage. Either Listeria monocytogenes and Listeria innocua were present in food samples as natural contaminants or L monocytogenes was added in the laboratory. Listeria repair broth (LRB), buffered Listeria enrichment broth, Listeria enrichment broth (LEB), Fraser broth, and University of Vermont modified Listeria enrichment broth were used to recover Listeria cells. The effectiveness of these enrichment regimes was found to be dependent on the type of stresses the cells had been exposed to. After exposure to ethanol, recovery of L monocytogenes cells was inhibited in enrichment regimes involving a nonselective period of resuscitation. On exposure to acetic acid, there were no significant differences (P < 0.05) between any of the regimes used. With heat-stressed cells, LRB recovered significantly fewer (P < 0.05) cells than did any other medium. On exposure to osmotic stress (elevated sugar and salt concentrations), LEB recovered the fewest cells. The largest number of cells was recovered from frozen fish (Hoki [Macruronus novazelandiae]) fillets with LRB. No single enrichment regime was consistently the most effective.

Survival of Listeria monocytogenes attached to stainless steel surfaces in the presence or absence of Flavobacterium spp.

Contaminated surfaces of food processing equipment are believed to be a significant source of Listeria monocytogenes to foods. However, very little is known about the survival of Listeria in processing environments. In a mixed bacterial biofilm of L. monocytogenes and Flavobacterium spp., the number of L. monocytogenes cells attaching to stainless steel increased significantly compared to when L. monocytogenes was in a pure culture. The L. monocytogenes cells in the mixed biofilms were also recoverable for significantly longer exposure periods. On colonized coupons held at 15 degrees C and 75% humidity, decimal reduction times were 1.2 and 18.7 days for L. monocytogenes in pure and mixed biofilms, respectively. With increasing exposure time, the proportion of cells that were sublethally injured (defined as an inability to grow on selective agar) increased from 8.1% of the recoverable cell population at day 0 to 91.4% after 40 days' exposure. At 4 and -20 degrees C, decimal reduction times for L. monocytogenes in pure culture were 2.8 and 1.4 days, respectively, and in mixed culture, 10.5 and 14.4 days, respectively. The enhanced colonization and survival of L. monocytogenes on "unclean" surfaces increase the persistence of this pathogen in food processing environments, while the increase in the percentage of sublethally injured cells in the population with time may decrease the ability of enrichment regimes to detect it.

Application of the Bigelow (z-value) model and histamine detection to determine the time and temperature required to eliminate Morganella morganii from seafood.

In New Zealand, the product most frequently implicated in cases of scombroid or histamine poisoning is the hot-smoked fish, kahawai (Arripis trutta). A properly controlled heating step in the production of hot-smoked seafood could eliminate bacteria able to convert the amino acid histidine to histamine. In this study, we determined the core temperatures and times required during hot smoking of kahawai to eliminate histamine-forming bacteria and to ensure a final product that will not produce histamine if subsequent temperature abuse occurs. Morganella morganii strains previously isolated from portions of hot-smoked kahawai with elevated histamine levels were inoculated onto product to be tested. A variation of the Bigelow or z-value model was used to generate a thermal death time graph, where the production of histamine, in a heat-treated and subsequently temperature-abused sample, was scored as a positive value (growth) and the absence of histamine was scored as a negative value (no growth). From a line fitted to the data, calculated times for the elimination of histamine-forming bacteria at test temperatures of 58, 59, 60, 61, and 62 degrees C were estimated to be 15.27, 8.81, 4.79, 2.68, and 1.46 min, respectively, giving a z value of 3.85 degrees C. This approach to thermal death determination, based on the presence or absence of a bacterial metabolite, proved to be an efficient way to determine the thermal regime required to eliminate bacteria capable of converting histidine to histamine on kahawai.

Survival of Listeria monocytogenes in sea water and effect of exposure on thermal resistance.

Survival, recoverability and sublethal injury of two strains of Listeria monocytogenes, Scott A and an environmental strain KM, on exposure to sea water at 12.8 or 20.8 degrees C was determined using in situ diffusion chambers. Plate counts were used to assess recoverability and injury while 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) reduction was used to determine respiratory activity. T90 values (times for 10-fold decreases in numbers of recoverable cells) on non-selective medium (trypticase soya agar with 0.6% yeast extract) at 12.8 and 20.8 degrees C were 61.7 and 69.2 h for L. monocytogenes Scott A, and 103.0 and 67.0 h for L. monocytogenes KM, respectively. On selective medium (Oxford agar), T90 values at 12.8 and 20.8 degrees C were 60.6 and 56.9 h for L. monocytogenes Scott A, and 83.0 and 65.9 h for L. monocytogenes KM, respectively. With Scott A, the percentage of sublethally injured cells at 12.8 and 20.8 degrees C was 1.7 and 17.7%, respectively, while for KM the values were 19.0 and 1.6%, respectively. The fraction of cells reducing CTC but which were not recoverable on plating progressively increased on exposure to sea water. Listeria monocytogenes KM challenged at 58 degrees C showed an apparent increase in heat resistance after exposure to sea water at 20.8 degrees C for 7 d (D58 = 2.64 min) compared with before exposure (D58 = 1.24). This increase in thermal resistance was not apparent at temperatures greater than 63 degrees C, and analysis of the best-fit regression lines fitted to the thermal data obtained from the two cell populations indicated that their thermal resistance was not significantly different (P > 0.05) over the temperature range tested (58-62 degrees C).

Thermal death times of Hafnia alvei cells in a model suspension and in artificially contaminated hot-smoked kahawai (Arripis trutta).

In New Zealand the product most frequently implicated in cases of scombroid poisoning is hot-smoked kahawai (Arripis trutta). Using a Hafnia alvei strain, previously isolated from a portion of hot-smoked kahawai with a histamine level of 1,659.4 mg/kg, thermal death trials were carried out in a model suspension (0.1% peptone) at 54, 55, 56, 57, and 58 degrees C. From the linear regression line (R2 = 0.98) fitted to observed D values plotted against temperature, calculated D values for 54, 55, 56, 57, and 58 degrees C were estimated to be 0.63, 0.36, 0.20, 0.11, and 0.06 min, respectively, giving a z value of 4.14 degrees C. Thermal death trials were also carried out for H. alvei associated with hot-smoked kahawai at 54, 55, 55.5, 56, and 57 degrees C. From the linear regression line (R2 = 0.93) fitted to the data, calculated D values for 54, 55, 56, and 57 degrees C were estimated to be 1.42, 0.74, 0.38, and 0.20 min, respectively, giving a z value of 3.57 degrees C. Results indicate that hot smoking has the potential to eliminate H. alvei from seafood products.

Reducing total aerobic counts and Listeria monocytogenes on the surface of king salmon (Oncorhynchus tshawytscha).

A trial industrial-scale fin-fish washing system was assessed for its effectiveness in removing bacteria associated with the skin of gilled and gutted king salmon (Oncorhynchus tshawytscha). Exposure of the salmon to 200 ppm free chlorine at a turnover rate for the total volume of the wash solution of 2.25 cycles h-1 for 120 min resulted in decreases in the aerobic plate count (APC) recovered from the salmon ranging from 96.6 to 99.2%. In order to optimize the washing regime a laboratory-scale fin-fish washing system was developed. Twenty-six washing treatments were used to generate a model to relate efficacy of bacterial removal with chlorine concentration, flow rate, and duration of washing. The model gave two local maxima of percentage APC reduction, one of 99.3% at a concentration of 126.3 ppm chlorine with a turnover of 0.75 cycle h-1 and a duration of 71.3 min and a second of 100.6% at a concentration of 126.3 ppm chlorine with a turnover of 3.75 cycles h-1 and a duration of 120 min. In additional experiments, it was determined that washing could eliminate 99.79% of Listeria monocytogenes cells that had been artificially inoculated onto the surface of gilled and gutted salmon. It was concluded that while chlorinated wash regimens have the potential to reduce the carriage of bacteria, including L. monocytogenes, into fish-processing facilities, they will not ensure an L. monocytogenes-free product. Further, the use of such a system has to be assessed with regard to allowable chlorine levels (subject to regulation), the effect of washing on the quality of the finished product, and the cost of water purchase and disposal.

HIV/AIDS in resource-poor settings: comprehensive care across a continuum.

BACKGROUND: The scale of the HIV pandemic in many resource-poor settings (RPS) has overwhelmed the already impoverished health and social support systems. OBJECTIVE: To propose a feasible and applicable model of care which can be used at district level in RPS faced with the prospect of caring for increasing numbers of persons living with HIV and AIDS (PWA) requiring care, and to outline some of the immediate challenges and directions for research. METHODS: Using Zambia as a test case, a review of existing community and health institution-based care programmes and facilities was made, and opportunities missed in meeting the demands of PWA were identified. RESULTS: Many opportunities have been missed both in encouraging PWA to enter the care continuum and in strengthening existing care services. An affordable and accessible model of care at district level that is not dependent on expensive drugs or medical interventions is suggested, using Zambia as an example. The model requires changes in the structure, function and HIV/AIDS care messages that are in line with new knowledge about the disease. CONCLUSION: This model of cooperation and sharing between health and social public/private and voluntary systems can be developed over time at a district level within existing resources, even as the pattern of the epidemic alters and resources become more available and better managed.

Efficacy of marinades against Listeria monocytogenes cells in suspension or associated with green shell mussels (Perna canaliculus).

In order to determine the listericidal efficacies of three marinades used in the production of marinated green shell mussels (Perna canaliculus), decimal reduction times (D values) were determined for a mixture of seven strains of Listeria monocytogenes exposed to marinades in the presence and absence of mussels. With an acetic acid (1.5%, wt/vol) marinade, calculated D values in the presence and absence of mussels were 77.3 and 33.3 h, respectively. Likewise, for an acetic acid (0.75%)-lactic acid (0.75%) marinade and an acetic acid (1.5%)-Glucono Delta-Lactone (0.2%)-based marinade, the D values in the presence and absence of mussels were 125.5 and 26.9 h and 86.3 and 19.3 h, respectively. Various increases in decimal reduction times in the presence of mussels indicated that there was no simple relationship between the listericidal natures of these marinades and the presence of mussels. This result suggests that difficulties may occur in trying to relate acid inhibition studies carried out in model broth systems to "real food" systems.

Infiltrative clival pituitary adenoma of ectopic origin.

An ectopic pituitary adenoma is a rare entity that may occur in several anatomic locations, the sphenoid sinus being the most common. Many of these tumors are amenable to surgical resection by means of a transsphenoidal approach. A more aggressive surgical approach is needed to attempt resection of extensive tumors that involve the clivus and the nasopharynx. Complete resection in these areas cannot always be guaranteed or determined, necessitating postoperative radiotherapy. Many different tumors of the sphenoid sinus and skull base can resemble ectopic pituitary adenomas on radiologic assessments. Because of this, preoperative endocrine assessment is recommended.

Scalp hair patterns in mental subnormality.

Scalp hair patterns have been examined in 1901 healthy subjects and 1789 severely subnormal patients. Patients with Down's syndrome had a highly significant excess of midline occipital whorls and a deficit of right-sided occipital whorls. Five out of 44 patients with microcephaly had a distinct 'up-sweep' of the frontal hair, a much lower proportion than found previously. Patients with unspecified mental subnormality had a highly significant deficit of multiple occipital whorls. Cutis verticis gyrata was noted incidentally in 15 subnormal patients, 13 of whom were males. Observation of hair patterns in individual patients with mental subnormality is of theoretical interest but is unlikely to be of great practical value.